Does this even need asking?
From your comment, you have only looked at consoles and asked if graphics can get better.
Point one: They already have compared to that, and by a fair amount. Go on a PC, and there is a massive jump in how games look - assuming the game was designed to look great on the PC, unlike most games released these days.
Beyond that, graphics exist at a near 'perfect' level in expensive CGI rendering that is not possible in real time ATM. Get to the photorealistic stage rendered in real time at 60+ FPS, and then there might be an argument as to whether or not they could get better.
As is, graphics are laughably terrible compared to what is possible. You look at a screenshot of a game and it takes you less than an instant to decide whether its real life or pre-rendered. Textures are too low res and don't have enough detail, models use low poly counts so they're able to be rendered on consoles and miss out on things such as wrinkles in someone's clothes thanks to this, hair is just a blob with lines painted on it, and its rare that it even reacts to physics like real hair, almost nothing has a unique shape - it is instead just a copy of something else in that scene.
Can graphics get any better?
Easily. When you get to the point of looking at your screen and being able to be forgiven for thinking that it was just a glass pane, and instead of your wall behind it there was a portal to anther world only visible from one side, that is when this question should be asked. Until then, yes, graphics can get better, and they likely will.